Organic electroluminescent device

ABSTRACT

An organic electroluminescent device comprising: a pair of electrodes; and at least one organic compound layer between the pair of electrodes, the at least one organic compound layer including a light emitting layer, wherein the light emitting layer contains at least one host material and at least one luminescent material, and the host material is a compound represented by the formula (I) as defined herein.

FIELD OF THE INVENTION

[0001] This invention relates to an organic electroluminescent device(hereinafter abbreviated as “OELD”) capable of converting electricalenergy into light to emit light. The OELD of the invention is suited foruse in the fields of display devices, displays, backlights, lightsources for illumination, recording, exposure or reading, signs orsignboards, interior decorations, optical communications, and so forth.

BACKGROUND OF THE INVENTION

[0002] OELDs have been actively studied and developed because of theircapabilities of emitting light of high brightness at a low drivingvoltage. An OELD generally comprises a pair of opposing electrodeshaving therebetween a light emitting layer or a plurality of organiclayers including a light emitting layer. With an electric field appliedto the opposing electrodes, electrons and positive holes are injectedfrom the cathode and the anode, respectively, into the light emittinglayer, where they are recombined to form excitons, which emit light.Otherwise, energy is transferred from the excitons to create excitons ofother molecules, which emit light. The light thus emitted from the lightemitting layer is utilized to display an image.

[0003] For the purpose of improving driving durability of OELDs, it hasbeen proposed to use a metal complex as a host material in the lightemitting layer as disclosed, e.g., in JP-A-2002-305083. There still hasbeen room for further improvement on efficiency and durability.

SUMMARY OF THE INVENTION

[0004] An object of the present invention is to provide an OELDexhibiting high luminance, high luminescence efficiency, andsatisfactory durability.

[0005] The object of the invention is accomplished by an OELD comprisinga pair of electrodes and at least one organic compound layer including alight emitting layer provided in between the electrodes, the lightemitting layer containing at least one host material and at least oneluminescent material, wherein the host material is a compoundrepresented by formula (I):

[0006] wherein X¹¹, X¹², X¹³, and X¹⁴ each represent a substituted orunsubstituted oxygen atom, a substituted or unsubstituted sulfur atom, asubstituted or unsubstituted nitrogen atom, a substituted orunsubstituted carbon atom or a substituted-or unsubstituted phosphorusatom; M¹¹ represents a metal ion; L¹¹ represents a ligand; Y¹¹represents a counter ion; m¹¹ represents an integer of 1 to 4; m¹²represents an integer of 0 to 6; m¹³ represents an integer of 0 to 4;and the X¹¹-X¹² bond, the X¹²-X¹³ bond, and the X¹³-X¹⁴ bond is a singlebond or a double bond; with the proviso that a compound in which theligand composed of X¹¹, X¹², X¹³, and X¹⁴ is one derived from an8-hydroxyquinolinol derivative is excluded.

[0007] The object is also accomplished by preferred embodiments of theabove-described OELD, in which:

[0008] (1) the luminescent compound is a phosphorescent compound thatemits light via a triplet excited state;

[0009] (2) the compound represented by formula (I) is a compoundrepresented by formula (IX):

[0010]  wherein M⁹¹ represents a metal ion; L⁹¹ represents a ligand; m⁹¹represents an integer of 1 to 4; m⁹² represents an integer of 0 to 6;Q⁹¹ represents an atomic group necessary to form a nitrogen-containingheterocyclic ring; and X⁹² and Q⁹² each represent an atomic groupnecessary to form a nitrogen-containing heterocyclic ring;

[0011] (3) the host material and the phosphorescent compound have a T₁value of 60 kcal/mol (251 kJ/mol) or higher, and the phosphorescentcompound emits phosphorescence having a peak wavelength (λ_(max)) of 550nm or shorter; or

[0012] (4) the at least one organic compound layer is at least threeorganic compound layers including a hole transporting layer, a lightemitting layer, and an electron transporting layer, and the electrontransporting layer has an IP value of 5.9 eV or higher.

[0013] (5) the host material is a compound represented by formula (II):

[0014]  wherein M²¹ represents a metal ion; L²¹ represents a ligand; m²¹represents an integer of 1 to 4; m²² represents an integer of 0 to 6;X²¹ represents an oxygen atom or a substituted nitrogen atom; X²²represents a substituted or unsubstituted carbon atom or a substitutednitrogen atom; X²⁴ represents a substituted nitrogen atom, a substitutedphosphorus atom or an oxygen atom; and R²⁴ represents a substituted orunsubstituted carbon atom or a substituted nitrogen atom;

[0015] (6) the host material is a compound represented by formula (III):

[0016]  wherein X³¹ represents an oxygen atom or a substituted nitrogenatom; X³² represents a substituted or unsubstituted carbon atom or asubstituted nitrogen atom; M³¹ represents a metal ion; L³¹ represents aligand; m³¹ represents an integer of 1 to 4; m³² represents an integerof 0 to 6; R³¹ represents a substituent; and X³⁵ represents asubstituted carbon atom or a substituted nitrogen atom;

[0017] (7) the host material is a compound represented by formula (IV):

[0018]  wherein M⁴¹ represents a metal ion; L⁴¹ represents a ligand; m⁴¹represents an integer of 1 to 4; m⁴² represents an integer of 0 to 6;X⁴¹ represents an oxygen atom or a substituted nitrogen atom; X⁴⁴represents a nitrogen atom or a phosphorus atom; R⁴⁴, R⁴⁵, R⁴⁶, and R⁴⁷each represent a hydrogen atom or a substituent; and R⁴² and R⁴³ eachrepresent a substituent;

[0019] (8) the host material is a compound represented by formula (V):

[0020]  wherein X⁵¹ represents an oxygen atom or a substituted nitrogenatom; X⁵² represents a substituted or unsubstituted carbon atom or asubstituted nitrogen atom; M⁵¹ represents a metal ion; L⁵¹ represents aligand; m⁵¹ represents an integer of 1 to 4; m⁵² represents an integerof 0 to 6; and Q⁵¹ represents a group necessary to form anitrogen-containing heterocyclic ring;

[0021] (9) the host material is a compound represented by formula (VI):

[0022]  wherein X⁶¹ represents an oxygen atom or a substituted nitrogenatom; X62 represents a substituted or unsubstituted carbon atom or asubstituted nitrogen atom; M⁶¹ represents a metal ion; L⁶¹ represents aligand; m⁶¹ represents an integer of 1 to 4; m⁶² represents an integerof 0 to 6; and Q⁶¹ represents a group necessary to form anitrogen-containing heterocyclic ring;

[0023] (10) the host material is a compound represented by formula(VII):

[0024]  wherein X⁷¹ represents an oxygen atom or a substituted nitrogenatom; X⁷² represents a substituted or unsubstituted carbon atom or asubstituted nitrogen atom; M⁷¹ represents a metal ion; L⁷¹ represents aligand; R⁷⁴ represents a substituted or unsubstituted carbon atom or asubstituted nitrogen atom; m⁷¹ represents an integer of 1 to 4; m⁷²represents an integer of 0 to 6;

[0025] (11) the host material is a compound represented by formula(VIII):

[0026]  wherein X⁸¹ represents an oxygen atom or a substituted nitrogenatom; M⁸¹ represents a metal ion; L⁸¹ represents a ligand; R⁸², R⁸³,R⁸⁴, R⁸⁵, R⁸⁶ and R⁸⁷ each represent a hydrogen atom or a substituent;m⁸¹ represents an integer of 1 to 4; and m⁸² represents an integer of 0to 6;

[0027] (12) the host material is a compound represented by formula (IX):

[0028]  wherein M⁹¹ represents a metal ion; L⁹¹ represents a ligand; m⁹¹represents an integer of 1 to 4; m⁹² represents an integer of 0 to 6;Q⁹¹ represents an atomic group necessary to form a nitrogen-containingheterocyclic ring; and X⁹² and Q⁹² each represent an atomic groupnecessary to form a nitrogen-containing heterocyclic ring.

[0029] (13) the host material is a compound represented by formula (X):

[0030]  wherein M¹⁰¹ represents a metal ion; L¹⁰¹ represents a ligand;Q¹⁰¹ represents a group necessary to form a nitrogen-containingheterocyclic ring; m¹⁰¹ represents an integer of 1 to 4; m¹⁰² representsan integer of 0 to 6; and X¹⁰² represents a substituted or unsubstitutedalkylene group, a carbonylene group or a sulfonylene group;

[0031] (14) the host material is a compound represented by formula (XI):

[0032]  wherein M¹¹¹ represents a metal ion; L¹¹¹ represents a ligand;m¹¹¹ represents an integer of 1 to 4; m¹¹² represents an integer of 0 to6; and R¹¹¹, R¹¹², R¹¹³, R¹¹⁴, R¹¹⁵, and R¹¹⁶ each represent a hydrogenatom or a substituent;

[0033] (15) the at least one host material is at least two hostmaterials;

[0034] (16) at least one of the host materials is an arylaminederivative;

[0035] (17) at least one of the host materials is an aromatichydrocarbon compound;

[0036] (18) at least one of the host materials is an aromaticnitrogen-containing heterocyclic compound; or

[0037] (19) at least one of the host materials is a metal complex otherthan the compound represented by formula (I).

DETAILED DESCRIPTION OF THE INVENTION

[0038] The OELD of the present invention is a device having at least oneorganic compound layer (also called an organic layer) including a lightemitting layer between a pair of electrodes, an anode and a cathode. Thelight emitting layer contains at least one host material and at leastone luminescent compound. The OELD is characterized in that the hostmaterial is a compound represented by formula (I).

[0039] The terminology “host material” as used herein means a compoundwhich primarily performs a function of injecting and/or transportingcharges in the light emitting layer and which per se does notsubstantially emit light. The host material concentration in the lightemitting layer is preferably 50 to 99.9% by weight, desirably 70 to99.8% by weight, more desirably 80 to 99.7% by weight, most desirably 90to 99.5% by weight.

[0040] In formula (I), X¹¹, X¹², X¹³, and X¹⁴ each represent an oxygenatom, a sulfur atom, a nitrogen atom, a carbon atom or a phosphorusatom, each of which may have a substituent. The substituents on X¹¹,X¹², X¹³, and X¹⁴ may be taken together to form a cyclic structure, suchas a hydrocarbon ring (e.g., benzene, pyridine, pyrazole, imidazole oroxazole) or a heterocyclic ring.

[0041] Where X¹¹, X¹², X¹³ or X¹⁴ is a substituted carbon atom, thesubstituents of the carbon atom include an alkyl group (preferablyhaving 1 to 30 carbon atoms, still preferably 1 to 20 carbon atoms,particularly preferably 1 to 10 carbon atoms, such as methyl, ethyl,isopropyl, t-butyl, n-octyl, n-decyl, n-hexadecyl, cyclopropyl,cyclopentyl or cyclohexyl), an alkenyl group (preferably having 2 to 30carbon atoms, still preferably 2 to 20 carbon atoms, particularlypreferably 2 to 10 carbon atoms, such as vinyl, allyl, 2-butenyl or3-pentenyl), an alkynyl group (preferably having 2 to 30 carbon atoms,still preferably 2 to 20 carbon atoms, particularly preferably 2 to 10carbon atoms, such as propargyl or 3-pentynyl), an aryl group(preferably having 6 to 30 carbon atoms, still preferably 6 to 20 carbonatoms, particularly preferably 6 to 12 carbon atoms, such as phenyl,p-methylphenyl, naphthyl or anthranyl), an amino group (preferablyhaving up to 30 carbon atoms, still preferably up to 20 carbon atoms,particularly preferably up to 10 carbon atoms, such as amino,methylamino, dimethylamino, diethylamino, dibenzylamino, diphenylaminoor ditolyamino), an alkoxy group (preferably having 1 to 30 carbonatoms, still preferably 1 to 20 carbon atoms, particularly preferably 1to 10 carbon atoms, such as methoxy, ethoxy, butoxy or 2-ethylhexyloxy),an aryloxy group (preferably having 6 to 30 carbon atoms, stillpreferably 6 to 20 carbon atoms, particularly preferably 6 to 12 carbonatoms, such as phenyloxy, 1-naphthyloxy or 2-naphthyloxy), aheterocyclic oxy group (preferably having 1 to 30 carbon atoms, stillpreferably 1 to 20 carbon atoms, particularly preferably 1 to 12 carbonatoms, such as pyridyloxy, pyrazyloxy, pyrimidyloxy or quinolyloxy), anacyl group (preferably having 1 to 30 carbon atoms, still preferably 1to 20 carbon atoms, particularly preferably 1 to 12 carbon atoms, suchas acetyl, benzoyl, formyl or pivaloyl), an alkoxycarbonyl group(preferably having 2 to 30 carbon atoms, still preferably 2 to 20 carbonatoms, particularly preferably 2 to 12 carbon atoms, such asmethoxycarbonyl or ethoxycarbonyl), an aryloxycarbonyl group (preferablyhaving 7 to 30 carbon atoms, still preferably 7 to 20 carbon atoms,particularly preferably 7 to 12 carbon atoms, such asphenyloxycarbonyl), an acyloxy group (preferably having 2 to 30 carbonatoms, still preferably 2 to 20 carbon atoms, particularly preferably 2to 10 carbon atoms, such as acetoxy or benzoyloxy), an acylamino group(preferably having 2 to 30 carbon atoms, still preferably 2 to 20 carbonatoms, particularly preferably 2 to 10 carbon atoms, such as acetylaminoor benzoylamino), an alkoxycarbonylamino group (preferably having 2 to30 carbon atoms, still preferably 2 to 20 carbon atoms, particularlypreferably 2 to 12 carbon atoms, such as methoxycarbonylamino), anaryloxycarbonylamino group (preferably having 7 to 30 carbon atoms,still preferably 7 to 20 carbon atoms, particularly preferably 7 to 12carbon atoms, such as phenyloxycarbonylamino), a sulfonylamino group(preferably having 1 to 30 carbon atoms, still preferably 1 to 20 carbonatoms, particularly preferably 1 to 12 carbon atoms, such asmethanesulfonylamino or benzenesulfonylamino), a sulfamoyl group(preferably having up to 30 carbon atoms, still preferably up to 20carbon atoms, particularly preferably up to 12 carbon atoms, such assulfamoyl, methylsulfamoyl, dimethylsulfamoyl or phenylsulfamoyl), acarbamoyl group (preferably having 1 to 30 carbon atoms, stillpreferably 1 to 20 carbon atoms, particularly preferably 1 to 12 carbonatoms, such as carbamoyl, methylcarbamoyl, diethylcarbamoyl orphenylcarbamoyl), an alkylthio group (preferably having 1 to 30 carbonatoms, still preferably 1 to 20 carbon atoms, particularly preferably 1to 12 carbon atoms, such as methylthio or ethylthio), an arylthio group(preferably having 6 to 30 carbon atoms, still preferably 6 to 20 carbonatoms, particularly preferably 6 to 12 carbon atoms, such asphenylthio), a heterocyclic thio group (preferably having 1 to 30 carbonatoms, still preferably 1 to 20 carbon atoms, particularly preferably 1to 12 carbon atoms, such as pyridylthio, 2-benzimidazolylthio,2-benzoxazolylthio or 2-benzothiazolylthio), a sulfonyl group(preferably having 1 to 30 carbon atoms, still preferably 1 to 20 carbonatoms, particularly preferably 1 to 12 carbon atoms, such as mesyl ortosyl), a sulfinyl group (preferably 1 having 1 to 30 carbon atoms,still preferably 1 to 20 carbon atoms, particularly preferably 1 to 12carbon atoms, such as methanesulfinyl or benzenesulfinyl), a ureidogroup (preferably having 1 to 30 carbon atoms, still preferably 1 to 20carbon atoms, particularly preferably 1 to 12 carbon atoms, such asureido, methylureido or phenylureido), a phosphoric acid amide group(preferably having 1 to 30 carbon atoms, still preferably 1 to 20 carbonatoms, particularly preferably 1 to 12 carbon atoms, such asdiethylphosphoramide or phenylphosphoramide), a hydroxyl group, amercapto group, a halogen atom (e.g., fluorine, chlorine, bromine oriodine), a cyano group, a sulfo group, a carboxyl group, a nitro group,a hydroxamic acid group, a sulfino group, a hydrazino group, an iminogroup, a heterocyclic group (containing a nitrogen atom, an oxygen atom,a sulfur atom, etc. as a hetero atom and preferably having 1 to 30carbon atoms, still preferably 1 to 12 carbon atoms, such as imidazolyl,pyridyl, quinolyl, furyl, thienyl, piperidyl, morpholino, benzoxazolyl,benzimidazolyl, benzothiazolyl, carbazolyl or azepinyl), a silyl group(preferably having 3 to 30 carbon atoms, still preferably 3 to 30 carbonatoms, particularly preferably 3 to 24 carbon atoms, such astrimethylsilyl or triphenylsilyl), a silyloxy group (preferably having 3to 40 carbon atoms, still preferably 3 to 30 carbon atoms, particularlypreferably 3 to 24 carbon atoms, such as trimethylsilyloxy ortriphenylsilyloxy), a group forming a carbonyl group, a group forming analkenyl group, and a group forming an imino group. These substituentsthat may be on the carbon atom will hereinafter be referred to as“substituents A”. The substituents A may each have a substituent.

[0042] Where X¹¹, X¹², X¹³ or X¹⁴ is a substituted nitrogen atom, thesubstituents of the nitrogen atom include an alkyl group, an alkenylgroup, an aryl group, a heteroaryl group, an acyl group (e.g., acetyl,benzoyl or trifluoroacetyl), a sulfonyl group (e.g., methanesulfonyl orpentafluorobenzenesulfonyl), a hydroxyl group, an alkoxy group, an aminogroup, an imino group, and a group forming an imino group. Thesesubstituents may have a substituent selected from, for example,substituents A.

[0043] Where X¹¹, X¹², X¹³ or X¹⁴ is a substituted phosphorus atom, thesubstituents of the phosphorus atom include an alkyl group, an alkenylgroup, an aryl group, a heteroaryl group, an acyl group, a sulfonylgroup, a hydroxyl group, an alkoxy group, an amino group, and an iminogroup. These substituents may have a substituent selected from, forexample, substituents A.

[0044] Where X¹⁴ is a substituted oxygen atom or a substituted sulfuratom, and X¹³-X¹⁴ bond is a single bond, the substituents of the oxygenatom or the sulfur atom include an alkyl group, an alkenyl group, anaryl group, a heteroaryl group, an acyl group, and a sulfonyl group.These substituents may have a substituent selected from, for example,substituents A.

[0045] X¹¹ is preferably an oxygen atom or a substituted nitrogen atom,still preferably an oxygen atom or a substituted nitrogen atom that isconnected to X¹² to form a nitrogen-containing heterocyclic ring,particularly preferably a substituted nitrogen atom that is connected toX¹² to form a nitrogen-containing heterocyclic ring.

[0046] X¹² is preferably a substituted or unsubstituted carbon atom or asubstituted nitrogen atom, still preferably a substituted orunsubstituted carbon atom, particularly preferably a carbonylene group,an alkylene group or a group that is connected to X¹¹ to form a cyclicstructure.

[0047] X¹³ is preferably a substituted carbon atom, a substitutednitrogen atom or a group that is connected to X¹⁴ to form a cyclicstructure, still preferably a group that is connected to X¹⁴ to form aheterocyclic ring, particularly preferably a group that is connected toX¹⁴ to form an aromatic nitrogen-containing heterocyclic ring.

[0048] X¹⁴ is preferably a substituted nitrogen atom, a substitutedphosphorus atom, an oxygen atom or a sulfur atom, still preferably asubstituted nitrogen atom, a substituted phosphorus atom or an oxygenatom, particularly preferably a substituted nitrogen atom, especiallypreferably a substituted nitrogen atom that is connected to X¹³ to forma nitrogen-containing heterocyclic ring.

[0049] The X¹¹-X¹² bond, the X¹²-X¹³ bond, and the X¹³-X¹⁴ bond are eacha single bond or a double bond. Whether the bond is single or double isnot matter of choice but is governed by whether the compound can existor not. For instance, when X¹¹ is an oxygen atom, a sulfur atom or asubstituted nitrogen atom, the X¹¹-X¹² bond should be single.

[0050] The X¹¹-X¹² bond and the X¹²-X¹³ bond are each preferably asingle bond, and the X¹³-X¹⁴ bond is preferably a double bond.

[0051] The metal species of the metal ion represented by M¹¹ includes,but is not limited to, alkali metals, alkaline earth metals, lanthanides(rare earth metals), transition metals, and typical metals. Preferredexamples of M¹¹ are ions of berylium, magnesium, aluminum, zinc, galliumor barium. A berylium ion, a magnesium ion, an aluminum ion or a zincion is still preferred. An aluminum ion or a zinc ion is particularlypreferred. A zinc ion is the most preferred.

[0052] The ligand represented by L¹¹ includes those described, e.g., inH. Yersin, Photochemistry and Photophysics of Coordination Compounds,Springer-Verlag, 1987 and Yamamoto Akio, Yukikinzokukagaku-kiso to ohyo,Shokabo Publishing Co., 1982. Preferred ligands include halogen ligands(e.g., Cl⁻ and F⁻), nitrogen-containing heterocyclic ligands (e.g.,bipyridyl, phenanthroline, phenylpyridine, pyrazolylpyridine, andbenzimidazolylpyridine), diketone ligands, nitrile ligands, CO ligands,isonitrile ligands, phosphorus ligands (e.g., phosphine derivatives,phosphorous ester derivatives, and phosphinine derivatives), carboxylicacid ligands (e.g., acetic acid ligand), aryloxy ligands (e.g., phenoxy,biphenyloxy, and cyanophenoxy), and siloxy ligands (e.g.,triphenylsiloxy). Still preferred are bidentate nitrogen-containingheterocyclic ligands (e.g., bipyridyl, phenanthroline, phenylpyridine,pyrazolylpyridine, benzimidazolylpyridine, and picolinic acid), diketoneligands (e.g., acetylacetone), aryloxy ligands, and siloxy ligands.Nitrogen-containing heterocyclic ligands are particularly preferred.

[0053] The counter ion represented by Y¹¹ preferably includes, but isnot limited to, alkali metal ions, alkaline earth metal ions, halideions, a perchlorate ion, a PF₆ ion, ammonium ions (e.g.,tetramethylammonium ion), a borate ion, and a phosphonium ion. Aperchlorate ion and a PF₆ ion are still preferred.

[0054] m¹¹ is an integer of 1 to 4, preferably 1 to 3. m¹² is an integerof 0 to 6, preferably 0 to 2, still preferably 0 or 1, particularlypreferably 0. m¹³ is an integer of 0 to 4, preferably 0 to 2, stillpreferably 0 or 1, particularly preferably 0.

[0055] From the ligands composed of X¹¹, X¹², X¹³, and X¹⁴ are excludedthose derived from 8-hydroxyquinolinol and derivatives thereof (e.g.,8-hydroxy-2-methylquinoline). It is preferred that X¹¹, X¹², X¹³, andX¹⁴ form ligands except those containing a quinoline ring.

[0056] The compound represented by formula (I) may have an additionalmetal ion on the ligand to form a polynuclear complex.

[0057] Of the compounds of formula (I) preferred are those representedby formulae (II), (III), and (IV) shown below, still preferred are thoseof formulae (V), (VI), (VII), and (VIII) shown below, particularlypreferred are those of formulae (IX) and (X) shown below. The mostpreferred are those of formula (XI) shown below.

[0058] The compounds of formulae (II) and (III) are preferred to thecompounds of formula (IV). The compounds of formula (II) are preferredto the compounds of formula (III).

[0059] In formula (II), M²¹, L²¹, m²¹, and m²² have the same meanings asM¹¹, L¹¹, m¹¹, and m¹², respectively (the preferred ranges for theformer are the same as for the latter); X²¹ represents an oxygen atom ora substituted nitrogen atom; X²² represents a substituted orunsubstituted carbon atom or a substituted nitrogen atom; X24 representsa substituted nitrogen atom, a substituted phosphorus atom or an oxygenatom; and R²⁴ represents a substituted or unsubstituted carbon atom or asubstituted nitrogen atom.

[0060] X²¹ is preferably an oxygen atom, a nitrogen atom substitutedwith an electron attracting group (e.g., acyl or sulfonyl) or asubstituted nitrogen atom that is connected to X²² to form anitrogen-containing heterocyclic ring, still preferably a substitutednitrogen atom that is connected to X²² to form a nitrogen-containingheterocyclic ring, particularly an azole ring (e.g., pyrazole, imidazoleor benzimidazole). A substituted nitrogen atom that is connected to X²²to form a monocyclic azole ring is particularly preferred.

[0061] X²² is preferably a substituted or unsubstituted carbon atom,still preferably a carbonylene group, an alkylene group or a groupconnected to X²¹ to form a nitrogen-containing heterocyclic ring,particularly preferably a carbonylene group or a group connected to X²¹to form an azole ring. A group connected to X²¹ to form a monocyclicazole ring is especially preferred.

[0062] X²⁴ is preferably a substituted nitrogen atom or an oxygen atom,still preferably a substituted nitrogen atom, particularly preferably asubstituted nitrogen atom that is connected to R²⁴ to form an aromaticnitrogen-containing heterocyclic ring (5- or 6-membered aromaticnitrogen-containing heterocyclic ring such as pyridine and benzoazole ispreferable), especially a 6-membered aromatic nitrogen-containingheterocyclic ring (e.g., pyridine).

[0063] R²⁴ is preferably a substituted carbon atom, still preferably asubstituted carbon atom that is connected to X²⁴ to form a cyclicstructure, particularly an aromatic nitrogen-containing heterocyclicring. A substituted carbon atom that is connected to X²⁴ to form a6-membered aromatic nitrogen-containing heterocyclic ring is especiallypreferred.

[0064] In formula (III), X²¹, X³², M³¹, L³¹, m³¹, and m³² have the samemeanings as X²¹, X²², M²¹, L²¹, m²¹, and m²², respectively (thepreferred ranges for the former are the same as for the latter); R³¹represents a substituent; and X³⁵ represents a substituted carbon atomor a substituted nitrogen atom.

[0065] The substituent represented by R³¹ includes those recited aboveas a substituent of the substituted nitrogen atom represented by X¹³.R³¹ is preferably a group that is connected to X³⁵ to form anitrogen-containing heterocyclic ring, particularly an aromaticnitrogen-containing heterocyclic ring, especially an pyrazole ring.

[0066] X³⁵ is preferably a group that is connected to R³¹ to form anitrogen-containing heterocyclic ring, particularly an aromaticnitrogen-containing heterocyclic ring, especially an pyrazole ring.

[0067] In formula (IV), M⁴¹, L⁴¹, m⁴¹, and m⁴² have the same meanings asM²¹, L²¹, m²¹, and m²², respectively (the preferred ranges for theformer are the same as for the latter); X⁴¹ represents an oxygen atom ora substituted nitrogen atom; X⁴⁴ represents a nitrogen atom or aphosphorus atom; R⁴⁴, R⁴⁵, R⁴⁶, and R⁴⁷ each represent a hydrogen atomor a substituent; R⁴⁴ and R⁴⁶ may be taken together to form acarbon-carbon double bond; R⁴⁵ and R⁴⁷ may be taken together to form acyclic structure (e.g., benzene ring); and R⁴² and R⁴³ each represent asubstituent.

[0068] X⁴¹ is preferably an oxygen atom or a nitrogen atom substitutedwith an electron attracting group, still preferably a nitrogen atomsubstituted with an electron attracting group, particularly preferably anitrogen atom substituted with an acyl group (e.g., acetyl,trifluoroacetyl or perfluorobenzoyl) or a sulfonyl group (e.g.,methanesulfonyl, trifluoromethanesulfonyl or benzenesulfonyl).

[0069] X⁴⁴ is preferably a phosphorus atom.

[0070] R⁴⁴, R⁴⁵, R⁴⁶, and R⁴⁷ are each preferably a hydrogen atom, analkyl group, an aryl group, a heterocyclic group, a group capable offorming a carbon-carbon double bond or a group capable of forming acyclic structure, still preferably a hydrogen atom, an alkyl group or agroup capable of forming a cyclic structure, particularly preferably agroup capable of forming a cyclic structure, especially a benzene ring.

[0071] R⁴² and R⁴³ are each preferably an alkyl group, an aryl group ora heterocyclic group, still preferably an alkyl group or an aryl group,particularly preferably an aryl group.

[0072] Of the compounds represented by formula (I), preferred are thoserepresented by formulae (V) to (VIII) shown below. The compounds offormulae (V), (VI), and (VII) are preferred to those of formula (VIII).The compounds of formulae (V) and (VI) are preferred to those of formula(VII). The compounds of formula (V) are preferred to those of formula(VI).

[0073] In formula (V), X⁵¹, X⁵², M⁵¹, L⁵¹, m⁵¹, and m⁵² have the samemeanings as X²¹, X²², M²¹, L²¹, m²¹, and m²², respectively (thepreferred ranges for the former are the same as for the latter); and Q⁵¹represents a group necessary to form a nitrogen-containing heterocyclicring (preferably a monocyclic nitrogen-containing heterocyclic ring or a5- or 6-membered condensed nitrogen-containing heterocyclic ring).

[0074] The nitrogen-containing heterocyclic ring completed by Q⁵¹ ispreferably an aromatic one. The aromatic nitrogen-containing ringpreferably includes a pyrrole ring, a pyrazole ring, an imidazole ring,a triazole ring, an oxazole ring, a thiazole ring, an oxadiazole ring, athiadiazole ring, a pyridine ring, a pyrazine ring, a pyrimidine ring,and a condensed ring thereof (e.g., benzoxazole or imidazopyridine),still preferably a pyrrole ring, a pyrazole ring, an imidazole ring, atriazole ring, an oxazole ring, a thiazole ring, an oxadiazole ring, athiadiazole ring, a pyridine ring, a pyrazine ring, a pyrimidine ring,and a 5- or 6-membered condensed ring thereof (e.g., benzoimidazole orimidazopyridine), particularly preferably a pyrazole ring, an imidazolering, a pyridine ring, and a 5- or 6-membered condensed ring thereof. Apyridine ring and a 5- or 6-membered condensed ring thereof are the mostpreferred.

[0075] In formula (VI), X⁶¹, X⁶², M⁶¹, L⁶¹, m⁶¹, and m⁶² have the samemeanings as X²¹, X²², M²¹, L²¹, m²¹, and m²², respectively (thepreferred ranges for the former are the same as for the latter); and Q⁶¹represents a group necessary to form a nitrogen-containing heterocyclicring (preferably a monocyclic nitrogen-containing heterocyclic ring).

[0076] The nitrogen-containing heterocyclic ring completed by Q⁶¹ ispreferably an aromatic one. The aromatic nitrogen-containing ringpreferably includes a pyrazole ring, a triazole ring, an oxadiazolering, a thiadiazole ring, and a condensed ring thereof, still preferablya pyrazole ring and a triazole ring, particularly preferably a pyrazolering.

[0077] In formula (VII), X⁷¹, X⁷², M⁷¹, L⁷¹, R⁷⁴, m⁷¹, and m⁷² have thesame meanings as X²¹, X²², M²¹, L²¹, R²⁴, m²¹ and m²², respectively (thepreferred ranges for the former are the same as for the latter).

[0078] In formula (VIII), X⁸¹, M⁸¹, L⁸¹, R⁸², R⁸³, R⁸⁴, R⁸⁵, R⁸⁶, R⁸⁷,m⁸¹, and m⁸² have the same meanings as X²¹, M²¹, L²¹, R⁴², R⁴³, R⁴⁴,R⁴⁵, R⁴⁶, R⁴⁷, m²¹, and m²², respectively (the preferred ranges for theformer are the same as for the latter).

[0079] The compounds of formula (I) preferably include those representedby formula (IX) and (X) shown below. The compounds of formula (IX) arepreferred to those of formula (X).

[0080] In formula (IX), M⁹¹, L⁹¹, Q⁹¹, m⁹¹, and m⁹² have the samemeanings as M²¹, L²¹, Q⁵¹, m²¹, and m²², respectively (the preferredranges for the former are the same as for the latter); and X⁹² and Q⁹²each represent an atomic group necessary to form a nitrogen-containingheterocyclic ring (preferably a monocyclic nitrogen-containing ring).

[0081] The nitrogen-containing heterocyclic ring completed by X⁹² andQ⁹² is preferably an aromatic one, still preferably a pyrrole ring, apyrazole ring, an imidazole ring, a triazole ring, or a condensed ringthereof, particularly preferably a monocyclic pyrrole ring, a monocyclicpyrazole ring or a monocyclic imidazole ring. A monocyclic pyrazole ringis the most preferred.

[0082] In formula (X), M¹⁰¹, L¹⁰¹, Q¹⁰¹, m¹⁰¹, and m¹⁰² have the samemeanings as M²¹, L²¹, Q⁵¹, m²¹, and m²², respectively (the preferredranges for the former are the same as for the latter); and X¹⁰²represents a substituted or unsubstituted alkylene group, a carbonylenegroup or a sulfonylene group.

[0083] The substituent of the substituted alkylene group preferablyincludes an alkyl group and an aryl group. X¹⁰² is preferably analkylene group or a carbonylene group, still preferably a carbonylenegroup.

[0084] The compounds of formula (I) preferably include those representedby formula (XI):

[0085] wherein M¹¹¹, L¹¹¹, m¹¹¹, and m¹¹² have the same meanings as M²¹,L²¹, m²¹, and m²², respectively (the preferred ranges for the former arethe same as for the latter); and R¹¹¹, R¹¹², R¹¹³, R¹¹⁴, R¹¹⁵, and R¹¹⁶each represent a hydrogen atom or a substituent.

[0086] R¹¹¹ and R¹¹² are each preferably a hydrogen atom, an alkylgroup, an aryl group, a heterocyclic group, a cyano group, an alkoxygroup or a fluorine atom, with a hydrogen atom or an alkyl group beingstill preferred.

[0087] The host material of the present invention preferably has a glasstransition temperature of 100° to 500° C., still preferably 110° to 300°C., particularly preferably 120° to 250° C.

[0088] The light emitting layer contains at least one host material andat least one luminescent compound, and the at least one host material isthe compound of formula (I). The luminescent compound used in thepresent invention is a compound performing a light emitting function inthe light emitting layer. The luminescence may be either fluorescence orphosphorescence or both. The luminescent compound is preferably aphosphorescent compound which emits light from a triplet excited state.The luminescent material in the light emitting layer preferably consistsof one or more phosphorescent compounds.

[0089] Other host materials that can be used in combination with thecompound of formula (I) include arylamine derivatives (e.g.,triphenylamine derivatives and benzidine derivatives), aromatichydrocarbon compounds (e.g., triphenylbenzene derivatives, triphenylenederivatives, phenanthrene derivatives, naphthalene derivatives, andtetraphenylene derivatives), aromatic nitrogen-containing heterocycliccompounds (e.g., pyridine derivatives, pyrazine derivatives, pyrimidinederivatives, triazine derivatives, pyrazole derivatives, imidazolederivatives, oxazole derivatives, and pyrrole derivatives), and metalcomplexes (e.g., zinc complexes, aluminum complexes, and galliumcomplexes).

[0090] The luminescent compound concentration in the light emittinglayer is preferably 0.1 to 50% by weight, desirably 0.2 to 30% byweight, more desirably 0.3 to 20% by weight, most desirably 0.5 to 10%by weight.

[0091] The phosphorescent compound preferably includes, but is notlimited to, transition metal complexes capable of emittingphosphorescence from the triplet excited state. The center metal of thetransition metal complexes preferably includes iridium, platinum,rhenium, ruthenium, palladium, rhodium, and rare earth metals. Iridiumand platinum are still preferred. The ortho-carbometalated iridiumcomplexes having a difluorophenylpyridine ligand which are disclosed inJP-A-2002-235076, JP-A-2002-170684, and Japanese Patent Application Nos.2001-239281 and 2001-248165 and compounds represented by formula (XII)shown below are preferred.

[0092] wherein R¹²¹, R¹²², R¹²³, R¹²⁴, R¹²⁵, R¹²⁶, R¹²⁷, and R¹²⁷ eachrepresent a hydrogen atom or a substituent; L¹²¹ represents a ligand;m¹²¹ represents an integer of 1 to 3; and m¹²² represents an integer of0 to 4.

[0093] R¹²¹ is preferably a hydrogen atom or an alkyl group, stillpreferably a hydrogen atom. R¹²² is preferably a hydrogen atom, an alkylgroup or a fluorine atom, still preferably a fluorine atom. R¹²³ ispreferably a hydrogen atom, an alkyl group or a fluorine atom, stillpreferably a hydrogen atom or a fluorine atom. R¹²⁴ is preferably ahydrogen atom, an alkyl group or a fluorine atom, still preferably ahydrogen atom or a fluorine atom, particularly preferably a fluorineatom.

[0094] R¹²⁵, R¹²⁷, and R¹²⁸ are each preferably a hydrogen atom or analkyl group, still preferably a hydrogen atom. R¹²⁶ is preferably ahydrogen atom, an alkyl group, an alkoxy group or a substituted aminogroup (preferably dialkylamino or diarylamino, still preferablydialkylamino).

[0095] The ligand as L¹²¹ preferably includes a phosphorus ligand, acarbon monoxide ligand, a halogen ligand, a diketone ligand, and abidentate nitrogen-containing heterocyclic ligand (e.g.,phenylbenzoxazole, pyrazolylpyridine, triazolylpyridine, picolinic acidor a condensed ring thereof). A bidentate nitrogen-containingheterocyclic ligand is still preferred. A pyrazolylpyridine ligand, atriazolylpyridine ligand or a picolinic acid ligand is particularlypreferred. A pyrazolylpyridine ligand or a triazolylpyridine ligand isespecially preferred.

[0096] m¹²¹ is preferably 2 or 3, still preferably 2. Where m¹²¹ is 2 or3, the phenylpyridine ligands maybe the same or different.

[0097] m¹²² is preferably 0 to 2, still preferably 0 or 1, particularlypreferably 1.

[0098] The phosphorescent compounds described in the followingliterature are also preferably used in the invention: U.S. Pat. Nos.6,303,238B1 and 6,097,147, WO 00/57676, WO 00/70655, WO 01/08230, WO01/39234A2, WO 01/41512A1, WO 02/02714A2, WO 02/15645A1,JP-A-2001-247859, Japanese Patent Application No. 2000-33561,JP-A-2002-117978, Japanese Patent Application No. 2001-248165,JP-A-2002-235076, Japanese Patent Application No. 2001-239281,JP-A-2002-170684, EP 1211257, JP-A-2002-226495, JP-A-2002-234894,JP-A-2001-247859, JP-A-2001-298470, JP-A-2002-173674, JP-A-2002-203678,and JP-A-2002-203679.

[0099] The phosphorescence life time of the phosphorescent compound tobe used is not particularly limited but is preferably 1 ms or shorter,still preferably 100 μs or shorter, particularly preferably 10 μs orshorter, at room temperature.

[0100] It is preferred that the host material and the phosphorescentcompound have a T₁ value of 60 kcal/mol (251 kJ/mol) or higher and thatthe phosphorescent compound emits phosphorescence having a peakwavelength (λ_(max)) of 550 nm or shorter. It is still preferred thatthe host material and the phosphorescent compound have a T₁ value of 62kcal/mol (259 kJ/mol) or higher and that the phosphorescent compoundemits phosphorescence having a peak wavelength (λ_(max)) of 500 nm orshorter. It is particularly preferred that the host material and thephosphorescent compound have a T₁ value of 65 kcal/mol (272 kJ/mol) orhigher and that the phosphorescent compound emits phosphorescence havinga peak wavelength (λ_(max)) of 480 nm or shorter. It is the mostpreferred that the host material and the phosphorescent compound have aT₁ value of 65 kcal/mol (272 kJ/mol) or higher and that thephosphorescent compound emits phosphorescence having a peak wavelength(λ_(max)) of 470 nm or shorter.

[0101] It is preferred that the at least one organic compound layer beat least three organic compound layers including a hole transportinglayer, a light emitting layer, and an electron transporting layer andthat the electron transporting layer have an IP value of 5.9 eV orhigher, particularly 6.0 eV or higher, especially 6.1 eV or higher.

[0102] The host material and the luminescent compound may be either lowmolecular compounds or oligomeric or polymeric compounds. The oligomericor polymeric compounds preferably have a polystyrene equivalent weightaverage molecular weight of 1,000 to 5,000,000, particularly 2,000 to1,000,000, especially 3,000 to 100,000. The polymeric materials, whichmay be either homopolymers or copolymers, include polymers containingthe structure represented by formulae (I) through (XII) in the mainchain or the side chain thereof. The host material and the luminescentcompound are preferably low molecular compounds.

[0103] Specific but non-limiting examples of the compounds representedby formula (I) are shown below. In addition to the examples shown,polynuclear complexes composed of the ligands and metal ions used in thecompounds shown (e.g., complexes having two zinc atoms to which threepyrazolylpyridine ligands are coordinated) are also suitable.

[0104] Specific but non-limiting examples of the luminescent compoundswhich can be used in the present invention are shown below.

[0105] The compounds used in the invention can be synthesized throughvarious processes. For example, the compounds are obtained by allowing aligand as such or in a dissociated state and a metal compound to reactwith or without a solvent (e.g., halogen-containing solvents, alcohols,ethers, esters, ketones, nitrites or water) in the presence or absenceof a base (either organic or inorganic, e.g., sodium methoxide,potassium t-butoxide, triethylamine or potassium carbonate) at roomtemperature or under heat (microwaving as well as general heating iseffective).

[0106] The OELD according to the present invention is not limited bysystem configuration, driving mode, usage, and so forth.

[0107] The OELD of the invention preferably has a layer containing acompound having an IP of 5.9 eV or higher (particularly 6.0 eV orhigher) between the cathode and the light emitting layer. It is stillpreferred for the OELD to have an electron transporting layer having anIP of 5.9 eV or higher between the cathode and the light emitting layer.

[0108] Methods for forming an organic compound layer include, but arenot limited to, vacuum deposition by resistance heating or electronbeam, sputtering, molecular accumulation, wet coating (spray coating,dip coating, impregnation, roll coating, gravure coating, reversecoating, roll brush coating, air knife coating, curtain coating, spincoating, flow coating, bar coating, microgravure coating, air doctorcoating, blade coating, squeegee coating, transfer roll coating, kisscoating, casting, extrusion coating, wire bar coating, screen coating,etc.), ink jet method, printing, and transfer. From the standpoint offilm characteristics and ease of production, resistance heating vacuumdeposition, wet coating, and transfer are preferred.

[0109] The OELD may have a hole injecting layer, a hole transportinglayer, an electron injecting layer, an electron transporting layer, aprotective layer, and so forth in addition to the light emitting layer.Each of the additional layers may have functions other than the intendedone meant by the designation of the layer. Each layer can be formed ofvarious materials according to the purpose.

[0110] The light-extraction efficiency of the OELD according to thepresent invention can be improved by various known techniques, such assurface structuring of the substrate (for example, formation of a fineuneven pattern), controlling the refractive index of the substrate, ITOlayer or organic layer (s), and controlling the thickness of thesubstrate, ITO layer or organic layer(s). The improvement inlight-extraction efficiency leads to an increase of external quantumefficiency.

[0111] The OELD of the invention may be of a so-called top emissiontype, in which light is emitted from the anode side of the device.

[0112] The substrate which can be used in the OELD includes, but is notlimited to, inorganic materials, such as yttrium-stabilized zirconia andglass; polyesters, such as polyethylene terephthalate, polybutyleneterephthalate, and polyethylene naphthalate; and polymers, such aspolyethylene, polycarbonate, polyether sulfone, polyarylate, allyldiglycol carbonate, polyimide, polycycloolefins, norbornene resins,poly(chlorotrifluoroethylene), Teflon, and tetrafluoroethylene-ethylenecopolymers.

[0113] The OELD according to the present invention can be used incombination with a blue light emitting device utilizing singlet excitonsfor light emission.

[0114] The light emitting layer may have at least one laminatestructure. The number of layers to be stacked to form the light emittinglayer is preferably up to 50, still preferably 4 to 30, particularlypreferably 6 to 20.

[0115] The thickness of each layer constituting the light emittinglayer, while not particularly limited, is preferably 0.2 to 20 nm, stillpreferably 0.4 to 15 nm, particularly preferably 0.5 to 10 nm,especially preferably 1 to 5 nm.

[0116] The light emitting layer may have a plurality of domainstructures. The light emitting layer may have other domain structures.The diameter of each domain is preferably 0.2 to 10 nm, still preferably0.3 to 5 nm, particularly preferably 0.5 to 3 nm, especially preferably0.7 to 2 nm.

[0117] The anode supplies positive holes to a hole injecting layer, ahole transporting layer, a light emitting layer, etc. Materials makingup the anode include metals, alloys, metal oxides, electricallyconductive compounds, and mixtures thereof. Those having a work functionof 4 eV or higher are preferred. Examples of useful materials areelectrically conductive metal oxides, such as tin oxide, zinc oxide,indium oxide, and indium tin oxide (ITO); metals, such as gold, silver,chromium, and nickel; mixtures or laminates of these metals andconductive metal oxides; inorganic electrically conductive substances,such as copper iodide and copper sulfide; organic electricallyconductive substances, such as polyaniline, polythiophene, andpolypyrrole; and mixtures or laminates of these materials and ITO.Conductive metal oxides are preferred. ITO is especially preferred forits productivity, electrical conductivity, and transparency. Thethickness of the anode is decided appropriately according to thematerial and usually ranges from 10 nm to 5 μm, preferably 50 nm to 1μm, still preferably 100 to 500 nm.

[0118] The anode is usually used as formed on a substrate, such as asoda lime glass plate, an alkali-free glass plate or a transparent resinplate. When a glass substrate is chosen, alkali-free glass is preferredfor avoiding leaching of ions from glass. In using soda lime glass, onehaving a barrier coat of silica, etc. is preferred. The thickness of thesubstrate is not particularly limited as long as the device can maintainmechanical strength. A glass substrate, for example, usually has athickness of 0.2 mm or larger, preferably 0.7 mm or larger.

[0119] The anode is formed by an appropriate technique selectedaccording to the material. For instance, an ITO layer is formed byelectron beam deposition, sputtering, resistance heating vacuumdeposition, chemical reaction (e.g., a sol-gel process), coating with anITO dispersion, and the like.

[0120] The anode thus formed may be subjected to cleaning or a liketreatment for reducing the driving voltage or increasing luminescenceefficiency. For an ITO anode, for instance, a UV-ozone treatment or aplasma treatment is effective.

[0121] The cathode supplies electrons to an electron injecting layer, anelectron transporting layer, a light emitting layer, etc. The materialmaking up the cathode is selected taking into consideration adhesion toan adjacent layer, such as an electron injecting layer, an electrontransporting layer or a light emitting layer, ionizing potential,stability, and the like. Useful materials include metals, alloys, metalhalides, metal oxides, electrically conductive compounds, and mixturesthereof. Examples of useful materials are alkali metals (e.g., Li, Na,and K) and fluorides or oxides thereof, alkaline earth metals (e.g., Mgand Ca) and fluorides or oxides thereof, gold, silver, lead, aluminum,sodium-potassium alloys or mixtures, lithium-aluminum alloys ormixtures, magnesium-silver alloys or mixtures, and rare earth metals(e.g., indium and ytterbium). Preferred of them are those having a workfunction of 4 eV or less, particularly aluminum, lithium-aluminum alloysor mixtures, and magnesium-silver alloys or mixtures. The cathode mayhave a single layer structure made of the above-recited material or alaminate structure containing the material. For example, analuminum/lithium fluoride laminate or an aluminum/lithium oxide laminateis preferred. The thickness of the cathode is selected appropriatelyaccording to the material and usually ranges from 10 nm to 5 μm,preferably 50 nm to 1 μm, still preferably 100 nm to 1 μm.

[0122] The cathode can be formed by electron beam deposition,sputtering, resistance heating vacuum deposition, wet coating, transfer,and like techniques. In vacuum deposition, a single metal may bedeposited, or two or more components may be deposited simultaneously. Aplurality of metals may be deposited simultaneously to form an alloycathode, or a previously formulated alloy may be deposited.

[0123] The anode and the cathode each preferably have as low sheetresistance as possible, particularly a sheet resistance lower thanseveral hundreds of ohms per square.

[0124] In addition to the host material and the luminescent compoundaccording to the present invention, the light emitting layer may furthercontain any other material as long as, with an electrical field applied,the layer performs a function of receiving holes from the anode or ahole injecting/transporting layer while receiving electrons from thecathode or an electron injecting/transporting layer, a function oftransporting the injected holes or electrons, and a function of asupplying a site for allowing the holes and the electrons to berecombined thereby emitting light. The other materials the lightemitting layer may contain include benzoxazole, benzimidazole,benzothiazole, styrylbenzene, polyphenyl, diphenylbutadiene,tetraphenylbutadiene, naphthylimide, coumarin, perylene, perinone,oxadiazole, aldazine, pyrralidine, cyclopentadiene, bisstyrylanthracene,quinacridone, pyrrolopyridine, thiadiazolopyridine, cyclopentadiene,styrylamine, aromatic dimethylidyne compounds; various metal complexes,such as 8-quinolinol metal complexes and rare earth complexes; polymers,such as polythiophene, polyphenylene, and polyphenylene vinylene;organosilanes; transition metal complexes, such astris(phenylpyridine)iridium and porphyrin platinum complexes; andderivatives of these compounds. The thickness of the light emittinglayer is not particularly limited and usually ranges from 1 nm to 5 μm,preferably 5 nm to 1 μm, still preferably 10 to 500 nm.

[0125] Methods of forming the light emitting layer include, but are notlimited to, vacuum deposition by resistance heating or electron beam,sputtering, molecular accumulation, wet coating, ink jet method,printing, LB method, and transfer. Resistance heating vacuum depositionand wet coating are preferred.

[0126] The OLED can have one or more light emitting layers. The two ormore light emitting layers may emit light of different colors to emit,for example, white light as a whole. A single light emitting layer canbe designed to emit white light.

[0127] The hole injecting layer and the hole transporting layer can beof any materials having a function of injecting holes supplied by theanode, a function of transporting the holes or a function of blockingthe electrons injected from the cathode. Examples of such materialsinclude carbazole, triazole, oxazole, oxadiazole, imidazole,polyarylalkanes, pyrazoline, pyrazolone, phenylenediamine, arylamines,amino-substituted chalcones, styrylanthracene, fluorenone, hydrazone,stilbene, silazane, aromatic tertiary amine compounds, styrylaminecompounds, aromatic dimethylidyne compounds, porphyrin compounds,polysilane compounds; conductive oligomers or polymers, such aspoly(N-vinylcarbazole), aniline copolymers, thiophene oligomers, andpolythiophene; organosilanes; carbon films; the compounds of the presentinvention; and derivatives of the recited compounds. The thickness ofthe hole injecting layer and the hole transporting layer is notparticularly limited and usually ranges from 1 nm to 5 μm, preferably 5nm to 1 μm, still preferably 10 to 500 nm. The hole injecting layer andthe hole transporting layer may each have a single layer structure madeof one or more of the above-recited materials or a multilayer structurecomposed of two or more layers having the same or differentcompositions.

[0128] The hole injection layer and the hole transporting layer can beformed by vacuum evaporation, LB method, wet coating with a solution ordispersion of the hole injecting/transporting material in a solvent, inkjet method, printing or transfer. Where wet coating techniques areadopted, it is possible to apply a resin component as dissolved ordispersed in the solvent together with the hole injecting/transportingmaterial. Applicable resin components include polyvinyl chloride,polycarbonate, polystyrene, polymethyl methacrylate, polybutylmethacrylate, polyester, polysulfone, polyphenylene oxide,polybutadiene, poly(N-vinylcarbazole), hydrocarbon resins, ketoneresins, phenoxy resins, polyamide, ethyl cellulose, polyvinyl acetate,ABS resins, polyurethane, melamine resins, unsaturated polyester resins,alkyd resins, epoxy resins, and silicone resins.

[0129] The electron injecting layer and the electron transporting layercan be made of any materials that perform at least one of a function ofinjecting electrons from the cathode, a function of transporting theelectrons, and a function of blocking positive holes from the anode.Such materials include triazole, oxazole, oxadiazole, imidazole,fluorenone, anthraquinodimethane, anthrone, diphenylquinone, thiopyrandioxide, carbodiimide, fluorenylidenemethane, distyrylpyrazine, aromatic(e.g., naphthalene or perylene) tetracarboxylic acid anhydrides,phthalocyanine; various metal complexes, such as metal complexes of8-quinolinol derivatives, metallo-phthalocyanines, and metal complexeshaving benzoxazole or benzothiazole as a ligand; organosilanes; andderivatives of the recited compounds. The thickness of the electroninjecting layer and the electron transporting layer is not particularlylimited and usually ranges from 1 nm to 5 μm, preferably 5 nm to 1 μm,still preferably 10 to 500 nm. The electron injecting layer and theelectron transporting layer may each have a single layer structure madeof one or more of the above-recited materials or a multilayer structurecomposed of two or more layers having the same or differentcompositions.

[0130] The electron injecting layer and the electron transporting layercan be formed by vacuum evaporation, LB method, wet coating with asolution or dispersion of the electron injecting/transporting materialin a solvent, ink jet method, printing, transfer or like techniques.Where wet coating techniques are adopted, it is possible to apply aresin component as dissolved or dispersed in the solvent together withthe hole injecting/transporting material. Applicable resin componentsinclude those described above with respect to the holeinjecting/transporting layers.

[0131] The protective layer can be of any material that preventssubstances which may accelerate deterioration of the device, such asmoisture and oxygen, from entering the device. Such materials includemetals, e.g., In, Sn, Pb, Au, Cu, Ag, Al, Ti, and Ni; metal oxides,e.g., MgO, SiO, SiO₂, Al₂O₃, GeO, NiO, CaO, BaO, Fe₂O₃, Y₂O₃, and TiO₂;metal fluorides, e.g., MgF₂, LiF, AlF₃, and CaF₂; nitrides, e.g.,SiN_(x) and SiO_(x)N_(y); polyethylene, polypropylene, polymethylmethacrylate, polyimide, polyurea, polytetrafluoroethylene,polychlorotrifluoroethylene, polydichlorodifluoroethylene,chlorotrifluoroethylene-dichlorodifluoroethylene copolymers,tetrafluoroethylene copolymers, fluorine-containing copolymers having acyclic structure in the main chain thereof; water absorbing substanceshaving a water absorption of at least 1%; and moisture-proof substanceshaving a water absorption of 0.1% or less.

[0132] Methods for forming the protective layer include, but are notlimited to, vacuum evaporation, sputtering, reactive sputtering,molecular beam epitaxy, cluster ion beam-assisted deposition, ionplating, plasma polymerization (radiofrequency-excited ion plating),plasma-enhanced CVD, laser-assisted CVD, thermal CVD, gas source CVD,wet coating techniques, printing, and transfer.

EXAMPLES

[0133] The present invention will now be illustrated in greater detailwith reference to Examples, but it should be understood that the presentinvention is not deemed to be limited thereto.

Comparative Example 1

[0134] N,N′-Diphenyl-N,N′-di(m-tolyl)benzidine (TPD) was deposited on acleaned ITO substrate by vacuum evaporation to a thickness of 50 nm.Compound B shown below (compound H-12 described in JP-A-2002-305083) andcompound (12-1) were vacuum co-deposited on the TPD layer at a weightratio of 34:2 to a deposition thickness of 36 nm. Compound A shown belowwas vacuum deposited thereon to a thickness of 36 nm. A pattern mask(having a pattern giving a light-emitting area of 4 mm by 5 mm) was puton the thus formed organic thin film, and cathodic deposition was made(lithium fluoride was vacuum deposited to a thickness of about 1 nm, andaluminum was then vacuum deposited to a thickness of about 200 nm) tocomplete a device. On applying a constant DC voltage to the resultingOLED by use of Source-Measure Unit Model 2400 supplied by Toyo Corp.,blue light emission was obtained. The luminance of the blue lightemission was measured with a luminance meter BM-8 supplied by Topcon. Asa result, EL_(max) was 489 nm, and the external quantum efficiency was2.5%.

Example 1

[0135] An OELD was prepared in the same manner as in Comparative Example1, except for replacing compound B with compound (1-1) of the presentinvention. As a result, the device emitted blue light having an EL_(max)of 489 nm, an external quantum efficiency of 7%, and a maximum luminanceof 15000 cd/m². The half decay time of an initial luminance of 1000cd/m² was twice or more that of Comparative Example 1.

Example 2

[0136] An OELD was prepared in the same manner as in Example 1, exceptfor replacing compound (12-1) with compound (12-3). As a result, thedevice emitted blue light having an EL_(max) of 465 nm and an externalquantum efficiency of 5%.

Example 3

[0137] Copper phthalocyanine was vacuum deposited on a cleaned ITOsubstrate to a deposit thickness of 10 nm.4,4′-Bis[N-(1-napthyl)-N-phenyl-amino]biphenyl (NPD) was depositedthereon to a thickness of 50 nm. Compound (1-1), compound C shown below,and Ir(ppy)₃ were co-deposited at a weight ratio of 7:7:1 on the NPDlayer. Compound D shown below was then deposited to a thickness of 36nm. Finally, a cathode was formed in the same manner as in ComparativeExample 1 to produce an OELD. The device emitted green light having anEL_(max) of 515 nm and an external quantum efficiency of 7%. The halfdecay time of an initial luminance of 100 cd/m² was about three timesthat of Comparative Example 1.

[0138] Similarly to Examples 1 and 2, OELDs achieving high luminescenceefficiency were prepared by using other compounds of the presentinvention.

[0139] The OELD according to the present invention has a high luminance,high luminescence efficiency, and satisfactory durability. Use of aphosphorescent compound that emits light from the triplet excited statein the light emitting layer brings about increase in luminance andluminescence efficiency.

[0140] This application is based on Japanese Patent application JP2002-382453, filed Dec. 27, 2002, the entire content of which is herebyincorporated by reference, the same as if set forth at length.

What is claimed is:
 1. An organic electroluminescent device comprising:a pair of electrodes; and at least one organic compound layer betweenthe pair of electrodes, the at least one organic compound layerincluding a light emitting layer, wherein the light emitting layercontains at least one host material and at least one luminescentmaterial, and the host material is a compound represented by the formula(I):

wherein X¹¹, X¹², X¹³, and X¹⁴ each independently represent asubstituted or unsubstituted oxygen atom, a substituted or unsubstitutedsulfur atom, a substituted or unsubstituted nitrogen atom, a substitutedor unsubstituted carbon atom or a substituted or unsubstitutedphosphorus atom; M¹¹ represents a metal ion; L¹¹ represents a ligand;Y¹¹ represents a counter ion; m¹¹ represents an integer of 1 to 4; m¹²represents an integer of 0 to 6; m¹³ represents an integer of 0 to 4;and the X¹¹-X¹² bond, the X¹²-X¹³ bond, and the X¹³-X¹⁴ bond is a singlebond or a double bond; with the proviso that a compound in which theligand composed of X¹¹, X¹², X¹³, and X¹⁴ is one derived from an8-hydroxyquinolinol derivative is excluded.
 2. The organicelectroluminescent device of claim 1, wherein the luminescent compoundis a phosphorescent compound that emits light via a triplet excitedstate.
 3. The organic electroluminescent device of claim 2, wherein thehost material and the phosphorescent compound have a T₁ value of 60kcal/mol or higher, and the phosphorescent compound emitsphosphorescence having a peak wavelength of 550 nm or shorter.
 4. Theorganic electroluminescent device of claim 1, wherein the at least oneorganic compound layer is at least three organic compound layersincluding a hole transporting layer, a light emitting layer, and anelectron transporting layer, and the electron transporting layer has anIP value of 5.9 eV or higher.
 5. The organic electroluminescent deviceof claim 1, wherein the host material is a compound represented byformula (II)

wherein M²¹ represents a metal ion; L²¹ represents a ligand; m²¹represents an integer of 1 to 4; m²² represents an integer of 0 to 6;X²¹ represents an oxygen atom or a substituted nitrogen atom; X²²represents a substituted or unsubstituted carbon atom or a substitutednitrogen atom; X²⁴ represents a substituted nitrogen atom, a substitutedphosphorus atom or an oxygen atom; and R²⁴ represents a substituted orunsubstituted carbon atom or a substituted nitrogen atom.
 6. The organicelectroluminescent device of claim 1, wherein the host material is acompound represented by the formula (III):

wherein X³¹ represents an oxygen atom or a substituted nitrogen atom;X³² represents a substituted or unsubstituted carbon atom or asubstituted nitrogen atom; M³¹ represents a metal ion; L³¹ represents aligand; m³¹ represents an integer of 1 to 4; m³² represents an integerof 0 to 6; R³¹ represents a substituent; and X³⁵ represents asubstituted carbon atom or a substituted nitrogen atom.
 7. The organicelectroluminescent device of claim 1, wherein the host material is acompound represented by the formula (IV):

wherein M⁴¹ represents a metal ion; L⁴¹ represents a ligand; m⁴¹represents an integer of 1 to 4; m⁴² represents an integer of 0 to 6;X⁴¹ represents an oxygen atom or a substituted nitrogen atom; X⁴⁴represents a nitrogen atom or a phosphorus atom; R⁴⁴, R⁴⁵, R⁴⁶, and R⁴⁷each independently represent a hydrogen atom or a substituent; and R⁴²and R⁴³ each independently represent a substituent.
 8. The organicelectroluminescent device of claim 1, wherein the host material is acompound represented by the formula (V):

wherein X⁵¹ represents an oxygen atom or a substituted nitrogen atom;X⁵² represents a substituted or unsubstituted carbon atom or asubstituted nitrogen atom; M⁵¹ represents a metal ion; L⁵¹ represents aligand; m⁵¹ represents an integer of 1 to 4; m⁵² represents an integerof 0 to 6; and Q⁵¹ represents a group necessary to form anitrogen-containing heterocyclic ring.
 9. The organic electroluminescentdevice of claim 1, wherein the host material is a compound representedby the formula (VI):

wherein X⁶¹ represents an oxygen atom or a substituted nitrogen atom;X⁶² represents a substituted or unsubstituted carbon atom or asubstituted nitrogen atom; M⁶¹ represents a metal ion; L⁶¹ represents aligand; m⁶¹ represents an integer of 1 to 4; m⁶² represents an integerof 0 to 6; and Q⁶¹ represents a group necessary to form anitrogen-containing heterocyclic ring.
 10. The organicelectroluminescent device of claim 1, wherein the host material is acompound represented by the formula (VII):

wherein X⁷¹ represents an oxygen atom or a substituted nitrogen atom;X⁷² represents a substituted or unsubstituted carbon atom or asubstituted nitrogen atom; M⁷¹ represents a metal ion; L⁷¹ represents aligand; R⁷⁴ represents a substituted or unsubstituted carbon atom or asubstituted nitrogen atom; m⁷¹ represents an integer of 1 to 4; m⁷²represents an integer of 0 to
 6. 11. The organic electroluminescentdevice of claim 1, wherein the host material is a compound representedby the formula (VIII):

wherein X⁸¹ represents an oxygen atom or a substituted nitrogen atom;M⁸¹ represents a metal ion; L⁸¹ represents a ligand; R⁸², R⁸³, R⁸⁴, R⁸⁵,R⁸⁶, and R⁸⁷ each represent a hydrogen atom or a substituent; m⁸¹represents an integer of 1 to 4; and m⁸² represents an integer of 0 to6.
 12. The organic electroluminescent device of claim 1, wherein thehost material is a compound represented by the formula (IX):

wherein M⁹¹ represents a metal ion; L⁹¹ represents a ligand; m⁹¹represents an integer of 1 to 4; m⁹² represents an integer of 0 to 6;Q⁹¹ represents an atomic group necessary to form a nitrogen-containingheterocyclic ring; and X⁹² and Q⁹² each independently represent anatomic group necessary to form a nitrogen-containing heterocyclic ring.13. The organic electroluminescent device of claim 1, wherein the hostmaterial is a compound represented by the formula (X):

wherein M¹⁰¹ represents a metal ion; L¹⁰¹ represents a ligand; Q¹⁰¹represents a group necessary to form a nitrogen-containing heterocyclicring; m¹⁰¹ represents an integer of 1 to 4; m¹⁰² represents an integerof 0 to 6; and X¹⁰² represents a substituted or unsubstituted alkylenegroup, a carbonylene group or a sulfonylene group.
 14. The organicelectroluminescent device of claim 1, wherein the host material is acompound represented by the formula (XI):

wherein M¹¹¹ represents a metal ion; L¹¹¹ represents a ligand; m¹¹¹represents an integer of 1 to 4; m¹¹² represents an integer of 0 to 6;and R¹¹¹, R¹¹², R¹¹³, R¹¹⁴, R¹¹⁵, and R¹¹⁶ each independently representa hydrogen atom or a substituent.
 15. The organic electroluminescentdevice of claim 1, wherein the at least one host material is at leasttwo host materials.
 16. The organic electroluminescent device of claim15, wherein at least one of the host materials is an arylaminederivative.
 17. The organic electroluminescent device of claim 15,wherein at least one of the host materials is an aromatic hydrocarboncompound.
 18. The organic electroluminescent device of claim 15, whereinat least one of the host materials is an aromatic nitrogen-containingheterocyclic compound.
 19. The organic electroluminescent device ofclaim 15, at least one of the host materials is a metal complex otherthan the compound represented by the formula (I).